Hm, is that a general rule? My son is not yet in school, so I don't know what it is like these days.
Also "like pink" is different from owning the occasional pink thing. I suppose a boy who would dress exclusively in pink would stand out, and maybe the bullies would try to cut him down. Still, I suspect it is not a large scale problem - obviously I don't condone the actions of such bullies, I mean there are probably not that many boys who would prefer to dress all in pink. (I didn't research that, though - in any case everybody should be allowed to like/wear whatever they want).
I don't care if a boy would "stand out" by dressing all in pink. That's not a valid reason for children to beat up children. The problem is not the child who's standing out, the problem is the bully who wants to hurt another person.